Synergistic Interaction between Candida albicans and Commensal Oral Streptococci in a NovelIn VitroMucosal Model

Abstract

ABSTRACTCandida albicansis a commensal colonizer of the gastrointestinal tract of humans, where it coexists with highly diverse bacterial communities. It is not clear whether this interaction limits or promotes the potential ofC. albicansto become an opportunistic pathogen. Here we investigate the interaction betweenC. albicansand three species of streptococci from the viridans group, which are ubiquitous and abundant oral commensal bacteria. The ability ofC. albicansto form biofilms withStreptococcus oralis,Streptococcus sanguinis, orStreptococcus gordoniiwas investigated using flow cell devices that allow abiotic biofilm formation under salivary flow. In addition, we designed a novel flow cell system that allows mucosal biofilm formation under conditions that mimic the environment in the oral and esophageal mucosae. It was observed thatC. albicansand streptococci formed a synergistic partnership whereC. albicanspromoted the ability of streptococci to form biofilms on abiotic surfaces or on the surface of an oral mucosa analogue. The increased ability of streptococci to form biofilms in the presence ofC. albicanscould not be explained by a growth-stimulatory effect since the streptococci were unaffected in their growth in planktonic coculture withC. albicans. Conversely, the presence of streptococci increased the ability ofC. albicansto invade organotypic models of the oral and esophageal mucosae under conditions of salivary flow. Moreover, characterization of mucosal invasion by the biofilm microorganisms suggested that the esophageal mucosa is more permissive to invasion than the oral mucosa. In summary,C. albicansand commensal oral streptococci display a synergistic interaction with implications for the pathogenic potential ofC. albicansin the upper gastrointestinal tract.